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The first direct, precision measurement of the branching ratio for the d&cay of the q meson into two photons, B(II + Y-Y) = r(v + rr)/rt.t(v), is p resented. The systematic uncertainties are quite differexit than in previous indirect measurements. Using the SATURNE II proton beam and a " liquid-deuterium target, the q mesons Were produced in the reaction pd + 3He Q at 1.5 MeV above threshold, and tagged by the detection of the recoil 'He in the magnetic spectrometer SPESZ. The two decay photons were detected in two BGO electromagnetic calorimeters located at 65* left and right of the beam axis. A lead collimatqr placed in front of the right calorimeter defined the detector acceptance. The analysis yielded B(v -+ 77) = 0.3949 * O.O017(stat) zk 0,0030(syst).PACS number(s): 13.40.Hq, 14.40.Aq

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